In the first two parts in this series (Building a
High Performance LED Lighting System, Part 1)
and
Building a
High Performance LED Lighting System, Part 2)
we covered the building of an
extremely bright handheld spotlight or bike headlight, and a couple of different
approaches to building extremely bright red lights.
In this story, the last in the series, we look at
how you can flash high power LEDs, and then install a complete high power LED
lighting system on a Human Powered Vehicle.
Flashing High Powered LEDs
Whever attention needs to be gained, it’s normal
practice to flash LEDs. In addition to attracting the eye, flashing LEDs also
considerably drops battery consumption.
Let’s look at the second point. If the light has a
similar on and off time – say 1 second on, 1 second off – it is said to have a
50 per cent duty cycle. Straightaway, we’ve approximately halved the power
consumption of the light! But what if we drop the duty cycle of the flashes
below 50 per cent? In fact, what if we run a 20 per cent duty cycle? Now we’ve
saved about 80 per cent of the power!
But if the light is off for 80 per cent of the
time, will anyone see it? Yes they will – if you make the flashing frequency
high enough. In other words, a very short duration flash that occurs rapidly
will work brilliantly at getting attention but will have energy consumption far
lower than if the light was on continuously.
Therefore, we have a very specific requirement for
a flasher module: high frequency, low duty cycle and able to switch at least a
few amps (a typical current draw of a high power LED system).
The best way we’ve found to achieve this is to use
the Nitrous Fuel Mixture / Motor Speed Controller electronic kit – available
from Jaycar Electronics and the AutoSpeed Shop.
Despite its name, this kit is a very effective
light flasher with high power handling, a flash rate adjustable by altering the
value of one capacitor and a duty cycle that can be adjusted by turning the
on-board pot. We’ve run a full article on this kit – see
The Nitrous Fuel Controller - That's Also a Lot More!. The section of that
article subtitle ‘Pulsing’ describes the capacitor change that needs to be made.
We used a 2.2uF capacitor that gave a flash rate
of about 3 times per second and the on-board pot was set to give a duty cycle
(an ‘on’ time) of 20 per cent. Note that both of these values are entirely up to
you – to save even more battery power you can go for a shorter duty cycle, for
example.
Connections
The Nitrous Fuel Mixture / Motor Speed Controller
kit (perhaps we’ll now just call it the High Power LED Flasher kit!) has three
connections. Power and earth are obvious (and, incidentally, the kit will work
on lower voltages than specified – we use it on ~7.5V) but the ‘out’ terminal
isn’t so intuitive.
Loads on the kit (eg the LED you want to flash)
are wired between the supply voltage and the ‘out’ terminal. In other
words, the module is like a switch that connects to ground to turn the LED
on. Keep this in mind and you won’t have too many problems.
Complete LED Lighting System
I ride the pictured recumbent Human Powered
Vehicle, which I designed and built (see Air 150 Recumbent Trike, Part
1.) Much of my riding – perhaps a majority – is at night on unlit rural and
semi-rural roads. Good lights are absolutely vital – both to stop being run over
by cars and also to spot the wildlife that includes pythons as thick as my arm
that lie across the roads.
The headlight must illuminate the road
sufficiently for me to be able to ride down hills at up to 60 km/h (lots of
steep hills around here) and also be able to attract the attention of car
drivers. The tail-lights need to be visible for a long way – at least 400 metres
– and experience has shown that side-facing lights are also needed. (Without
side-facing lights I feel very vulnerable at T-junctions, where I am riding
across the top of the T and a car is approaching at right-angles.)
Finally, I expect to go touring on this machine
and want to be able to run the lights in day-time – they’re quite visible even
in direct sunshine. To achieve this, a good battery life is needed.
The lighting system consists of:
The 5W headlight covered in Part 1 Building a High Performance LED Lighting System, Part 1 of this series
Four 1W side and tail-lights, as covered in Part 2
Building a High Performance LED Lighting System, Part 2 of this
series. These comprise two yellow wide-angle lights, each facing sideways (these
use 20mm oval-beam collimators)...
...and two 30mm narrow beam red tail-lights facing
rearwards.
There’s also a NiMH battery pack and a control
system that flashes the side and rear lights and allows the headlight to be
easily switched from being fully on to flashing. Let’s have a look at the
battery and the control system.
The battery is one stick from a current model
Toyota Prius high voltage battery pack. It has a nominal capacity of 6.5
amp-hours and a voltage of 7.2V. It has a mass of 1kg and is 285 x 117 x 20mm.
The stick was obtained by buying a complete HV battery that came up on eBay at a
price too good to refuse. (The other sticks are being used in different
applications.)
The High Power LED Flasher kit is mounted in a
plastic box. Front and rear light connections are made via plugs and sockets,
allowing the battery/control box to be easily removed as required.
The LEDs are powered through dropping resistors –
all 1 ohm 5W units. The wattage rating is much higher than needed but it ensures
that the resistors do not get hot. By using a nominally 7.2V battery, very
little power is wasted in the resistors – the system is still highly efficient.
The rear/side lights are wired in a series/parallel arrangement (see below for
more on the wiring).
The control box has a large rocker on/off switch
positioned in its upper lid. The box is taped to the battery...
...and then the whole lot placed in this bag that is
strapped to the trike. The switch is able to be operated through the soft wall
of the bag.
A second switch is placed on a steering lever to
enable the selection of flashing or fully-on headlight modes. Flashing mode is
used in well-lit areas and in the daytime, or when the attention of a driver
needs to be gained. In night riding it is switched from one mode to the other
quite frequently. The side and tail-lights constantly flash.
Wiring
The wiring diagram is fairly straightforward. Note
the fuse placed close to the battery and the way that the headlight can be
switched from being connected straight to ground (ie always on) to being
switched so that it is grounded through the flashing unit (ie flashing). A
single pole, double throw (ie three pin) switch is used for this function. The
three 1 ohm resistors can also be seen, as can the series/parallel wiring of the
tail and side lights.
Conclusion
While not ultra lightweight, the complete HPV LED
lighting system is probably amongst the best in the world for illumination and
visibility at a relatively low power consumption. And the techniques covered in this
series are also applicable whenever very bright lighting with low power
consumption is needed.
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